1. Field of the Invention
The present invention relates to a file sharing device known as a file server or NAS (Network Attached Storage) and an inter-file sharing device data migration method.
2. Description of the Related Art
File servers are used in order for data to be shared between plural computer terminals dispersed on a network. As an early file server, a server where a file sharing protocol such as CIFS (Common Internet File System) or NFS (Network File System) is disposed in a versatile OS (Operating System) is known. As an improved file server, an NAS where a dedicated OS specializing in file sharing services is used to support plural file sharing protocols (CIFS, NFS, DAFS (Direct Access File System), etc.) is known.
The number of files to be shared and the number of clients using shared files have been increasing each year, and individual file sizes also continue to increase. In order to accommodate the increased demand for file sharing services, storage devices and communication lines are being strengthened and technology is switching over to high-performance file servers.
Several methods of causing data to migrate from old file servers to new file servers are known. A first method is a method that temporarily suspends file access from a client and occupies the migration source file server (old file server) and the migration destination file server (new file server) to carry out data copying between both file servers. A second method is a method that backs up data retained in the migration source file server and causes the migration destination file server to restore the backup data.
A third method that causes data to migrate without stopping the file sharing service is also known (JP-A-2000-173279). In this third method, when access is made by a client during data migration and data to which access has been requested is data that has already been copied to the migration destination file server, the data is provided from the migration destination file server to the client. Alternatively, when the data to which access has been requested is data that has not yet been copied to the migration destination file server, the data is provided from the migration destination file server to the client once the data has been copied from the migration source file server to the migration destination file server.
In the first method, the client cannot use the file sharing service until data migration is completed, because the migration source file server and the migration destination file server are occupied during the data migration. In a case where the amount of migration target data is relatively small, it is possible to resume the file sharing service for a short period. However, as the amount of data increases, the stopped time of the file sharing service increases.
In the second method, the file sharing service can be continued using the migration source file server while the backup data is being restored in the migration destination file server. However, when the client updates the data during restoration, a difference arises between the latest data of the migration source file server and the backup data. Thus, for example, an access log during restoration is kept and, after restoration is completed, the storage content of the migration destination file server is updated to the latest state on the basis of the access log. In this case, after restoration is completed, labor for synchronizing the storage contents between the migration destination file server and the migration source file server becomes necessary, and this takes time. As another method, providing a file sharing service in a read-only mode during restoration is also conceivable. However, this is not very convenient because the client can only read the data.
In the third method, the file sharing service can be provided to the client even during data migration. However, in the third method, in a case where the client requests access to data that has not yet been copied to the migration destination file server, the data is copied from the migration source file server to the migration destination file server and provided from the migration destination file server to the client. In other words, in the third method, the responsiveness of the service drops because the data to which access has been requested by the client is provided to the client after it is first copied to the migration destination file server. Also, in the third method, the configuration becomes complicated and costs also rise because it is necessary to dispose a data migration-dedicated interface in both of the migration source file server and the migration destination file server.